In modern flexographic liquid application systems, a transfer roll such as an anilox roll is wetted by a liquid, for example ink or an adhesive, and is rotated to apply the liquid to the surface of an adjacent rotating plate roll. The plate roll has a rubber surface which is shaped or engraved to pick up liquid from the transfer roll and to deposit the liquid in a desired pattern on the surface of an adjacent moving web of material.
In a gravure system, the transfer roll is an engraved printing cylinder which transfers liquid in a desired pattern directly onto the surface of a web of material. In such known systems, the transfer roll picks up the wetting liquid from a trough or "fountain" and rotates to meter a desired amount of liquid onto the adjacent plate roll or web of material.
Rapidly rotating transfer rolls in known apparatus typically fling excess liquid radially and axially of the transfer roll during the liquid application process. It is known to utilize fluid deflectors or "slingers" at the ends of the transfer roll to direct at least a portion of the liquid flung from the roll back into the underlying trough or fountain. A substantial amount of liquid is lost in this process and liquid is also easily splashed or sprayed over the driving mechanism of the transfer roll or even over the web. Also, the liquid in the trough may thicken as a result of evaporation or contamination.
In U.S. Pat. No. 4,590,855 to Schommer et al. entitled Reverse Angle Doctor Blade Assembly with Stationary End Seal, a liquid transfer apparatus is disclosed which includes a transfer roll with stationary end seal support rings held in stationary sliding relation to the ends of the roll by spring biased pins. A reverse angle doctor blade assembly is positioned adjacent to the transfer roll to uniformly meter a wetting liquid to the moving surface of the roll.
The doctor blade assembly includes a reservoir which is held in liquid communication with the surface of the transfer roll. End seals of the reservoir sealingly engage the stationary end seal supports to provide a liquid seal between the reservoir and the transfer roll.
The end seals of the reservoir result in a rather complicated structure of this closed reservoir chamber whose shape will be characterized by corners which counteract effective washing of said liquid, such as ink or an adhesive by flushing, e.g., in connection with change of ink.
Accordingly, it is an object of the invention to provide a reservoir chamber without sharp corners and edges to which the ink may adhere during flushing.
Another object of the invention is to provide a reservoir chamber having a simpler structure than the known one and having a very small volume.
A further object of the invention is to provide a reservoir chamber which is completely sealed and which results in an extra large contact face between inks and transfer roll and therefore ensures dyeing at high rates.